The prescription of Methotrexate is well-recognized for various neoplastic diseases. For Rheumatoid arthritis, it is prescribed once a week, low-dose regimen for the treatment of psoriasis and rheumatoid arthritis. Apart from providing therapeutic benefit, it is not devoid of side effects like oral ulceration which may be due to over dosage regarding its once-weekly regime. This case report describes a patient with inherent Methotrexate toxicity that developed oral mucositis due to Methotrexate being given for rheumatoid arthritis.